feat(cargo): add vendored-libgit2 feature (#3426)

* feat(cargo): add vendored-libgit2 feature

this is done to resolve the issues when the host system doesn't have
`libgit2` installed or if its incompatible with the version we expect

see: sharkdp/bat/issues/2939

* docs(changelog): add vendored libgit2 entry

CHANGELOG.md

@@ -36,6 +36,7 @@
 - Update console dependency to 0.16, see #3351 (@musicinmybrain)
 - Fixed some typos #3244 (@ssbarnea)
 - Update onig_sys dependency to 69.9.1 to fix a gcc build failure #3400 (@CosmicHorrorDev)
+- Add a cargo feature (`vendored-libgit2`) to build with vendored libgit2 version without depending on the system's one #3426 (@0x61nas)
 
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